27 Just then his disciples returned and were surprised to find him talking with a woman. But no one asked, "What do you want?" or "Why are you talking with her?"
28 Then, leaving her water jar, the woman went back to the town and said to the people, 29 "Come, see a man who told me everything I ever did. Could this be the Christ?" 30 They came out of the town and made their way toward him.
31 Meanwhile his disciples urged him, "Rabbi, eat something."
32 But he said to them, "I have food to eat that you know nothing about."
33 Then his disciples said to each other, "Could someone have brought him food?"
34 "My food," said Jesus, "is to do the will of him who sent me and to finish his work. 35 Do you not say, 'Four months more and then the harvest'? I tell you, open your eyes and look at the fields! They are ripe for harvest. 36 Even now the reaper draws his wages, even now he harvests the crop for eternal life, so that the sower and the reaper may be glad together. 37 Thus the saying 'One sows and another reaps' is true. 38 I sent you to reap what you have not worked for. Others have done the hard work, and you have reaped the benefits of their labor."
There is a constant theme in the gospels of people understanding things in the physical realm and then Jesus elevating their understanding to the spiritual/eternal. The woman was talking about water at a well. Jesus talked about living water, salvation. His disciples talked about harvesting food in the field. Jesus talked about harvesting souls. When Jesus speaks of sending people out to the harvest, he is sending them to go spread the gospel to a lost and dying world.